The present invention relates to a composite sliding material containing a polytetrafluoroethylene resin as the main component, and particularly to a composite sliding material directed to improvement of fretting wear resistance when used as a bearing material.
Plain bearing materials for use without any lubrication include, for example, materials comprising a back metal layer and a sliding material layer comprising a synthetic resin as the main component provided on the surface side of the back metal layer. Such materials (sliding member compositions) are disclosed in JP-A-Sho 61 (1986)-266451 filed by the present applicants. The materials comprising a polytetrafluoroethylene resin (which will be hereinafter referred to as xe2x80x9cPTFExe2x80x9d) as the main component, other fluororesins, synthetic resins and a solid lubricant, have a low friction and a distinguished wear resistance.
Plain bearing comprising a synthetic resin (fluororesin) as a surface layer (sliding layer) is used as a bearing (bush) for supporting a throttle valve shaft in the engine throttle body, where the bush is exposed to fretting wear-susceptible situations of slight relative movements between two contact surfaces, different from the ordinary friction and wear. Said JP-A-Sho 61 (1986)-266451 takes no fretting wear into consideration and fails to teach any compositions of distinguished fretting wear resistance.
On the other hand, for example, JP-A-Hei 5 (1993)-339593 discloses a technique of improving the fretting wear resistance of plain bearing materials of PTFE series by adding an aromatic polyester resin and spherical carbon to PTFE. In the technique of JP-A-Hei 5 (1993)-339593 a satisfactory fretting wear resistance is however not always obtained because the hardness of spherical carbon is not enough and much spherical carbon falls out.
The present invention has been made in view of these situations and an object of the present invention is to provide a composite sliding material containing a polytetrafluoroethylene resin as the main component directed to improvement of fretting wear resistance when used as a bearing material.
Sliding materials of fluororesin (PTFE) series have a low friction and a low corrosion resistance (chemical resistance), and has such a merit that they can be used in a wide temperature range suitably without any lubrication, but the sliding materials of the conventional compositions have no satisfactory fretting wear resistance when exposed to fretting wear-susceptible situations. To enhance the fretting wear resistance, it is necessary to provide a composition capable of giving a tough and hard sliding material with a distinguished wear resistance against periodic repetitions of slight relative movements. As a result of extensive tests and studies to improve the fretting wear resistance of sliding materials of fluororesin (PTFE) series, the present inventors have successfully attained the present invention.
The present invention provides a composite sliding material, which comprises 1-25 vol.% of tetrafluoroethylene-perfluoroalkylvinyl ether copolymer resin (which will be hereinafter referred to as xe2x80x9cPFAxe2x80x9d), 1-25 vol.% of at least one member selected from the group consisting of oxybenzoylpolyester resin (which will be hereinafter referred to as xe2x80x9cPOBxe2x80x9d) and polyimide resin (which will be hereinafter referred to as xe2x80x9cPIxe2x80x9d) and 0.1-10 vol.% of hard particles, the balance being PTFE as the main component (first mode of the present invention).